A cutting insert and a cutting tool for shoulder milling have conventionally been known (see, for example, Japanese Patent Laying-Open No. 2013-121636). A main cutting edge is formed at the boundary portion between a first face, in which a hole for fixing the cutting insert is formed, and a second face, which is a lateral face adjacent to the first face. The main cutting edge may form a circular arc or a straight line when viewed from the first face side.